Absolute DatingAbsolute Dating

Absolute DatingAbsolute Dating

Absolute dating provides a Absolute dating provides a numerical age for the numerical age for the material tested, while material tested, while relative dating can only relative dating can only provide a sequence of age. provide a sequence of age.

It is a technique used to It is a technique used to date materials, usually date materials, usually based on a comparison based on a comparison between the amount of between the amount of original material and the original material and the amount of decayed amount of decayed material. material.

So how does it work?So how does it work?

Remember that…Remember that… All matter is made up All matter is made up

of elementsof elements All elements have an All elements have an

atomic number that atomic number that indicates the number indicates the number of protons in the of protons in the nucleusnucleus

Example…Example… Carbon has an atomic Carbon has an atomic

number of 6 (meaning it number of 6 (meaning it has 6 protons in its has 6 protons in its nucleus)nucleus)

Carbon also has 6 Carbon also has 6 neutrons in its nucleus, neutrons in its nucleus, so we call it Carbon 12 so we call it Carbon 12

6+6 = 12, right ?6+6 = 12, right ?

Chemistry Review Cont…Chemistry Review Cont… Sometimes, an element can have an unequal number of Sometimes, an element can have an unequal number of

protons and neutrons in it’s nucleus protons and neutrons in it’s nucleus The protons will stay the same, but the neutrons changeThe protons will stay the same, but the neutrons change If this is the case, we call it an isotopeIf this is the case, we call it an isotope Example…Example…

Carbon 12 = 6 protons, 6 neutronsCarbon 12 = 6 protons, 6 neutrons Carbon 13 = 6 protons, 7 neutronsCarbon 13 = 6 protons, 7 neutrons Carbon 14 = 6 protons, 8 neutronsCarbon 14 = 6 protons, 8 neutrons

Radiometric DatingRadiometric Dating

Some of these Some of these isotopes are isotopes are unstable, and can unstable, and can lose parts protons, lose parts protons, neutrons AND neutrons AND electrons (they electrons (they decay).decay).

They do so at a They do so at a constant rate, which constant rate, which can be recorded or can be recorded or observed.observed.

Radiometric Dating Cont…Radiometric Dating Cont… If you change the If you change the

number of protons or number of protons or neutrons, the element neutrons, the element changes.changes.

We call the original We call the original element the “parent” element the “parent” element, while the element, while the new element is known new element is known as the “daughter” as the “daughter” element.element.

Determining the ratio Determining the ratio of “parent” material to of “parent” material to “daughter” material is “daughter” material is Radiometric/Absolute Radiometric/Absolute Dating!Dating!

Half LifeHalf Life

Because it can take a long time for Because it can take a long time for the entire isotope to decay, scientists the entire isotope to decay, scientists can study how long it takes “half” of can study how long it takes “half” of the original amount to decay. the original amount to decay.

This is called its “This is called its “Half-LifeHalf-Life””

Common unstable substances Common unstable substances include…include…

Carbon 14 > NitrogenCarbon 14 > Nitrogen Uranium 238 > Lead 206Uranium 238 > Lead 206 Potassium > ArgonPotassium > Argon